Method and apparatus for determining process rate

ABSTRACT

A method for dry processing a substrate in a processing chamber is provided. The substrate is placed in the processing chamber. The substrate is dry processed, wherein the dry processing creates at least one gas byproduct. A concentration of the at least one gas byproduct is measured. The concentration of the at least one gas byproduct is used to determine processing rate of the substrate.

INCORPORATION BY REFERENCE

The present disclosure incorporates by reference the patent entitled,“APPARATUS FOR DETERMINING PROCESS RATE” by Albarede et al. filed on thesame date, U.S. patent Ser. No. 14/863,211, which is incorporated byreference for all purposes.

BACKGROUND

The present disclosure relates to the manufacturing of semiconductordevices. More specifically, the disclosure relates to etching used inmanufacturing semiconductor devices.

During semiconductor wafer processing, silicon containing layers areselectively etched.

SUMMARY

To achieve the foregoing and in accordance with the purpose of thepresent disclosure, a method for dry processing a substrate in aprocessing chamber is provided. The substrate is placed in theprocessing chamber. The substrate is dry processed, wherein the dryprocessing creates at least one gas byproduct. A concentration of the atleast one gas byproduct is measured. The concentration of the at leastone gas byproduct is used to determine processing rate of the substrate.

In another manifestation, a method for dry etching at least eightalternating layers over a substrate in a processing chamber is provided.The substrate is placed in the processing chamber. The at least eightalternating layers are dry etched, wherein the dry etching creates atleast one gas byproduct. A concentration of the at least one gasbyproduct is measured. The concentration of the at least one gasbyproduct is used to determine etch rate of the substrate, etchselectivity, and etch uniformity. A chamber parameter is changed basedon the measured concentration.

These and other features of the present disclosure will be described inmore detail below in the detailed description of the disclosure and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a high level flow chart of an embodiment.

FIG. 2 is a schematic view of a plasma processing chamber that may beused in an embodiment.

FIG. 3 is a computer system that may be used in an embodiment.

FIG. 4 is a more detailed flow chart of the surface reaction phase.

FIGS. 5A-F are graphs provided by an embodiment.

FIG. 6 is a high level flow chart of a method by which a substrate isused to measure the SiF₄.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present disclosure will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentdisclosure. It will be apparent, however, to one skilled in the art,that the present disclosure may be practiced without some or all ofthese specific details. In other instances, well known process stepsand/or structures have not been described in detail in order to notunnecessarily obscure the present disclosure.

Current technology used for process control (e.g. endpoint) relies onrelative measurements or indirect measurements of plasma parametersusing emission spectroscopy, reflectance, or RF voltage and current. Forendpoint control, optical emission spectroscopy reaches it limits withsignal changes tending to zero when CDs shrink below 21 nm and aspectratio increases beyond 30:1. For in-situ etch rate (ER) measurementsusing RF voltage/current are based on correlations that are not alwaysmaintained chamber to chamber.

An embodiment relies on absolute measurements of SiF₄ or SiBr₄, or SiCl₄or other SiX₄ byproducts that is a direct byproduct of most siliconcontaining etches (nitrides, oxides, poly, and silicon films) when usingfluorocarbon based chemistries. By combining the measurement with anetch model (SiF₄ mass balance based on XSEM images or a feature profilesimulation model calibrated with XSEM images), one can predict endpoint,ER as a function of depth, average wafer selectivity, and uniformity incertain conditions. The SiF₄ byproducts are detected using IR absorptionusing quantum cascade laser spectroscopy allowing parts per billionlevel detection for accurate predictions.

This disclosure describes a method that combines etch-profile modelingcoupled with SiF₄ IR-absorption to control the etch process. The methodallows the extension of endpoint capability beyond the reach oftradition methods, such as emission spectroscopy, in high-aspect ratioapplications such as DRAM cell-etch and 3D-NAND hole and trenchpatterning. The combination of absolute density measurement and etchprofile emission modeling allows one to additionally determine in-situetch process parameters such as ER, selectivity, and uniformity that canbe used to achieve run-to-run process matching.

In an embodiment, an etch process is characterized by measuring a directstable byproduct that can be used to determine: 1) Endpoint forhigh-aspect ratio DRAM and 3D-NAND etches for process/CD control, 2)Method to scale endpoint detection for future nodes, 3) Combined with amodel one can determine in-situ: a) Average wafer ER and ER as functionof depth (ARDE), b) An average wafer uniformity and selectivity, and c)Both measurements can be used for run-to-run matching and faultdetection, 4) Using high sensitivity quantum cascade laser spectroscopyto achieve ppb level limit of detection needed for accurate etchendpoint and etch parameters estimation.

To facilitate understanding, FIG. 1 is a high level flow chart of aprocess used in an embodiment. A substrate is placed in a processingchamber (step 104). The substrate is dry processed (step 108). Duringthe dry processing a gas byproduct is created. The concentration of thegas byproduct is measured (step 112). The measured concentration of thegas byproduct is used to determine processing rate, endpoint,uniformity, aspect ratio dependent etch rate, and selectivity (step116). Chamber settings are changed based on the measured concentrationof the gas byproduct (step 120). A determination is made on whether thedry process is complete (step 124). If the dry process is not completethe dry processing of the substrate 108 is continued by furthermeasuring the concentration of the byproduct and continuing the cycle.If the dry process is complete, then the process is stopped.

Examples

In an example of a preferred embodiment, a substrate with a siliconcontaining layer is placed in a processing chamber (step 104). FIG. 2schematically illustrates an example of a plasma processing chamber 200,which may be used to perform the process of etching a silicon containinglayer in accordance with one embodiment. The plasma processing chamber200 includes a plasma reactor 202 having a plasma processing confinementchamber 204 therein. A plasma power supply 206, tuned by a match network208, supplies power to a TCP coil 210 located near a power window 212 tocreate a plasma 214 in the plasma processing confinement chamber 204 byproviding an inductively coupled power. The TCP coil (upper powersource) 210 may be configured to produce a uniform diffusion profilewithin the plasma processing confinement chamber 204. For example, theTCP coil 210 may be configured to generate a toroidal power distributionin the plasma 214. The power window 212 is provided to separate the TCPcoil 210 from the plasma processing confinement chamber 204 whileallowing energy to pass from the TCP coil 210 to the plasma processingconfinement chamber 204. A wafer bias voltage power supply 216 tuned bya match network 218 provides power to an electrode 220 to set the biasvoltage on the substrate 204 which is supported by the electrode 220. Acontroller 224 sets points for the plasma power supply 206, gassource/gas supply mechanism 230, and the wafer bias voltage power supply216.

The plasma power supply 206 and the wafer bias voltage power supply 216may be configured to operate at specific radio frequencies such as, forexample, 13.56 MHz, 27 MHz, 2 MHz, 60 MHz, 200 kHz, 2.54 GHz, 400 kHz,and 1 MHz, or combinations thereof. Plasma power supply 206 and waferbias voltage power supply 216 may be appropriately sized to supply arange of powers in order to achieve desired process performance. Forexample, in one embodiment, the plasma power supply 206 may supply thepower in a range of 50 to 5000 Watts, and the wafer bias voltage powersupply 216 may supply a bias voltage of in a range of 20 to 2000 V. Fora bias up to 4 kV or 5 kV a power of no more than 25 kW is provided. Inaddition, the TCP coil 210 and/or the electrode 220 may be comprised oftwo or more sub-coils or sub-electrodes, which may be powered by asingle power supply or powered by multiple power supplies.

As shown in FIG. 2, the plasma processing chamber 200 further includes agas source/gas supply mechanism 230. The gas source 230 is in fluidconnection with plasma processing confinement chamber 204 through a gasinlet, such as a shower head 240. The gas inlet may be located in anyadvantageous location in the plasma processing confinement chamber 204,and may take any form for injecting gas. Preferably, however, the gasinlet may be configured to produce a “tunable” gas injection profile,which allows independent adjustment of the respective flow of the gasesto multiple zones in the plasma process confinement chamber 204. Theprocess gases and byproducts are removed from the plasma processconfinement chamber 204 via a pressure control valve 242 and a pump 244,which also serve to maintain a particular pressure within the plasmaprocessing confinement chamber 204. The gas source/gas supply mechanism230 is controlled by the controller 224. A Kiyo by Lam Research Corp. ofFremont, Calif., may be used to practice an embodiment. In otherexamples, a Flex by Lam Research Corp. of Fremont, Calif., may be usedto practice an embodiment.

In this embodiment, connected to an exhaust pipe 246 after the pump 244,a gas cell 232 is provided, into which exhaust gas flows. An IR lightsource 234 is positioned adjacent to a window in the gas cell 232, sothat an IR beam from the IR light source 234 is directed into the gascell 232. The IR beam can travel through the gas cell multiple times(typically >1 m) to achieve ppb level or even lower hundredth of pptdetection limits. The IR light is absorbed by the gas as it travelsinside the gas cell. An IR detector 236 is positioned adjacent toanother window in the gas cell 232 to measure the light absorptionlevel.

FIG. 3 is a high level block diagram showing a computer system 300,which is suitable for implementing a controller 224 used in embodiments.The computer system may have many physical forms ranging from anintegrated circuit, a printed circuit board, and a small handheld deviceup to a huge super computer. The computer system 300 includes one ormore processors 302, and further can include an electronic displaydevice 304 (for displaying graphics, text, and other data), a mainmemory 306 (e.g., random access memory (RAM)), storage device 308 (e.g.,hard disk drive), removable storage device 310 (e.g., optical diskdrive), user interface devices 312 (e.g., keyboards, touch screens,keypads, mice or other pointing devices, etc.), and a communicationinterface 314 (e.g., wireless network interface). The communicationinterface 314 allows software and data to be transferred between thecomputer system 300 and external devices via a link. The system may alsoinclude a communications infrastructure 316 (e.g., a communications bus,cross-over bar, or network) to which the aforementioned devices/modulesare connected.

Information transferred via communications interface 314 may be in theform of signals such as electronic, electromagnetic, optical, or othersignals capable of being received by communications interface 314, via acommunication link that carries signals and may be implemented usingwire or cable, fiber optics, a phone line, a cellular phone link, aradio frequency link, and/or other communication channels. With such acommunications interface, it is contemplated that the one or moreprocessors 302 might receive information from a network, or might outputinformation to the network in the course of performing theabove-described method steps. Furthermore, method embodiments mayexecute solely upon the processors or may execute over a network such asthe Internet in conjunction with remote processors that shares a portionof the processing.

The term “non-transient computer readable medium” is used generally torefer to media such as main memory, secondary memory, removable storage,and storage devices, such as hard disks, flash memory, disk drivememory, CD-ROM and other forms of persistent memory and shall not beconstrued to cover transitory subject matter, such as carrier waves orsignals. Examples of computer code include machine code, such asproduced by a compiler, and files containing higher level code that areexecuted by a computer using an interpreter. Computer readable media mayalso be computer code transmitted by a computer data signal embodied ina carrier wave and representing a sequence of instructions that areexecutable by a processor.

A dry process is performed on the substrate in the processing chamber,where the dry process creates at least one gas byproduct (step 108). Indifferent embodiments, either the substrate is a silicon wafer, which isetched, or one or more silicon containing layers over the substrate areetched. In this example, a stack of alternating silicon oxide andsilicon nitride layers is etched. Such an alternating stack of siliconoxide and silicon nitride is designated as ONON, which is used in 3Dmemory devices. In this example, there are at least eight alternatinglayers of ONON. In etching such a stack, both ER and selectivitydecrease with aspect ratio, meaning that the difference between etchrates of the silicon oxide and silicon nitride decreases as aspectratio, the ratio of the etch depth over the etch width, increases. Toetch such a stack an etch gas of C_(x)F_(y)H_(z)/O₂ is provided by thegas source 230. RF power is provided by the plasma power supply 206 tothe TCP coil 210 to form the etch gas into an etch plasma, which etchesthe stack and forms at least one gas byproduct, which in this example isSiF₄. (Other etch byproducts such as SiBr₄ or SiCl₄ can be monitoreddepending on the gas chemistry by tuning the IR light source to theabsorption band of each byproduct.)

During the dry process, the concentration of the at least one gasbyproduct is measured (step 112). In this embodiment, exhaust from thepump 244 flows to the gas cell 232. The IR light source 234 provides abeam of IR light into the gas cell 232. In this embodiment, sides of gascell are equipped with a set of highly reflective mirrors 232 to reflectthe beam of IR light a plurality of times before the beam of IR light isdirected to the IR detector 236, which measures the intensity of thebeam of IR light. The optical path length of the IR beam can reach fewmeters to few hundreds of meters thus allowing for sub ppb detectionlimit. Data from the IR detector 236 is sent to the controller 224,which uses the data to determine the concentration of the SiF₄.

The measured concentration is used to determine processing rate,endpoint, uniformity, and selectivity (step 116). FIG. 4 is a moredetailed flow chart of the step of using the measured concentration todetermine processing rate. A library of concentration models is provided(step 404). Such models may provide feature/wafer scale etch as afunction of aspect ratio, uniformity, and selectivity. Such models maybe generated by experiment or may be analytically calculated, or may bedetermined using both methods. In an example of a creation of a model,an etch may be provided where concentration of a gas byproduct ismeasured over time. Since this example uses an etch, the processing rateis an etch rate. The etched features are examined and measured. From themeasurements of the features and the measurement of the concentration ofbyproduct gas over time geometrical etch models and mass balancedequations may be used to determine etch rate, endpoint, uniformity, andselectivity. In one embodiment, a model would have a singleconcentration. In another embodiment, a model has a plurality ofconcentrations at various times. A plurality of measured concentrationsover time is then used to match the closest model (step 408). Theclosest model is then used to determine an etch rate (step 412). Theetch rate is the increase in the depth of etched features over time. Todetermine etch rate, endpoint, uniformity, and selectivity either asingle measurement or a plurality of measurements may be used. Theendpoint indicates when an etch is complete. This is may be determinedby when a stop layer is reached or a discontinuity in the signal isreached. As mentioned above, the aspect ratio is the ratio of the etchdepth over the etch width. The measured concentration may be used todetermine the evolution of ER and selectivity with aspect ratio of theetched features since CD evolution of the feature is extracted from themodel. Uniformity is a measurement of how evenly features are beingetched. Features may be etched at different rates depending on featurewidth or feature density, causing nonuniform etch rates. The measuredconcentration may be used to determine the uniformity of the etch rates.Selectivity is a measurement of the difference in the etch rate of onematerial versus the etch rate of another material. In this example, theselectivity may be the difference in the etch rate of silicon oxidecompared to silicon nitride for ONON or oxide to Poly for OPOPstructures. In the alternative, selectivity may be the different in theetch rate of the silicon oxide compared to the etch rate of a maskmaterial or a stop layer. The measured concentration may be used todetermine etch selectivity.

FIG. 5A is a graph 504 of the concentration of SiF₄ versus etch timewhen etching ONON stack. The alternating concentration is caused byetching the alternating nitride and oxide layers. The recipe in thisembodiment etches SiN faster than SiO. As a result, the peakconcentrations are when SiN is etched and the valleys are when SiO isetched. The times in between are transitions between SiN to SiO and viceversa. A touch down point 508 indicates the etch endpoint, when the lastSiO or SiN layer has been etched. From the locations of the peaks andvalleys, a selectivity of between 0.6:1 to 0.4:1 for the etch rate ofSiO:SiN can be derived. FIG. 5B shows a graph of the top criticaldimension tCD 512 and the bottom critical dimension bCD 516 of thefeatures extracted from the model. In FIG. 5B the solid lines are valuesof CDs at the center of the wafer, the dashed lines represent the CDs atthe edge of the wafer. From the top and bottom critical dimensions, theARDE coefficient may be determined. In this example, the ARDE isdetermined to be 0.05. Uniformity is calculated to be 1%. FIG. 5C is amagnified graph of the tCD. FIG. 5D is a graph of the slope of the rateconcentration SiF₄ versus time. The minimum and maximum concentrationsover time may be obtained from this graph. FIG. 5E shows a graph of etchrate versus time for SiN 532 and for SiO 536, which is obtained from thepeak and valley positions. Since depth increase with time, etch rateversus depth may be derived from the graphs. FIG. 5F is a graph 540 ofthe differences between the measured selectivity and a model.

Chamber settings are changed based on the measured concentration (step120). When the endpoint is not found using the measured concentration(step 124), the etch process is continued and the process is continuedback at step 112. If the etch stop is found, the etch may be stopped bystopping the flow of the etch gas and by stopping the power from theplasma power supply 206. If it is determined that the ER is too low,etch parameters such as gas or RF power may be changed to increase ER.If it is determined that the nonuniformity is too high, parameters suchas gas feed to different region the chamber or ESC zones temperaturesmay be changed to improve uniformity.

Etch process parameters, such as ER, can be used for advanced faultdetection to determine run-to-run and chamber-to-chamber performance bycorrelating them to on-wafer metrology parameters.

To achieve a high degree of accuracy in measuring the concentration ofthe etch byproducts, e.g. SiF₄, one needs to determine the contributionto the byproducts under various conditions of the chamber from that ofthe wafer being etched. A calibration method based on the use ofdifferent type substrates is used to deconvolute each contribution. FIG.6 is a high level flow chart of a method by which a substrate A made forinstance of photo-resist is placed in the chamber (step 604), thenprocess wear the concentration of SiF₄ is measured (step 604), which isthen used to determine the SiF₄ emission contribution from the chamber(612). Then an oxide wafer (substrate B) is introduced into theprocessing chamber (step 616) to measure the emission of SiF₄ from bothchamber and wafer for various power settings (step 620). By combiningthe concentration measurements and oxide ex-situ ER, one can calibratethe emission of SiF₄ with ER for each chamber. This calibration isrequired to achieve run-to-run and chamber-to-chamber process controland fault detection. Further calibration may be accomplished by removingthe substrate B and placing another substrate (substrate C) in theprocessing chamber (step 624). The concentration of byproducts ismeasured for the process at various power settings (step 628). Thecontribution from the substrates and the chamber are determined based onthe measurements (step 632). A calibration is established between theetch rate and byproduct concentration for the chamber (step 636).

Various embodiments may use generic geometric etch models based onmeasured profiles, such as XSEM profiles and/or simple mass balanceequations to allow the use of the measured concentration of byproductgas to determine processing rate, endpoint, uniformity, dependent ratioetch rate, or selectivity

Advantages of placing the gas cell after the exhaust pump are that thegas is denser in after the exhaust pump than the gas in the processingchamber. In addition, reflective surfaces are not exposed to the plasmain the processing chamber, so that reflective surfaces would not bedegraded by the plasma. In other embodiments, the gas cell is in theplasma processing chamber, such as surrounding the plasma region.

Various embodiments are useful for providing memory devices such as DRAMand 3D-NAND devices. In various embodiments the plasma process is anetch process of a silicon containing layer or a low-k dielectric layer.In various embodiments the RF power may be inductively coupled orcapacitively coupled. A Flex by Lam Research Corp. of Fremont, Calif.,may be used to practice an embodiment with capacitive coupling to etchDRAM and 3D NAND structures. In other embodiment, other types of plasmapower coupling may be used. In other embodiments, alternating layers ofsilicon oxide and polysilicon (OPOP) may be etched.

While this disclosure has been described in terms of several preferredembodiments, there are alterations, permutations, modifications, andvarious substitute equivalents, which fall within the scope of thisdisclosure. It should also be noted that there are many alternative waysof implementing the methods and apparatuses of the present disclosure.It is therefore intended that the following appended claims beinterpreted as including all such alterations, permutations, and varioussubstitute equivalents as fall within the true spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for dry processing a substrate in aprocessing chamber, comprising: creating a plurality of concentrationmodels related to processing rate and processing uniformity; placing thesubstrate in the processing chamber; dry processing the substrate,wherein the dry processing creates at least one gas byproduct; measuringa concentration of the at least one gas byproduct; fitting the measuredconcentration of the at least one gas byproduct over time to at leastone of the plurality of concentration models; using the concentration ofthe at least one gas byproduct to determine processing rate of thesubstrate; creating process parameters from the fitted at least one ofthe plurality of concentration models and the measured concentration ofthe at least one gas byproduct; using the created process parameters todetermine run-to-run and chamber-to-chamber performance; and using theconcentration of the at least one gas byproduct to determine processinguniformity.
 2. The method, as recited in claim 1, further comprisingusing the concentration of the at least one gas byproduct to determineprocess endpoint.
 3. The method, as recited in claim 2, wherein theprocess is plasma etching, and further comprising using theconcentration of the at least one gas byproduct to determine aspectratio dependent ER.
 4. The method, as recited in claim 3, wherein theprocess is plasma etching alternating layers, and further comprisingusing the concentration of the at least one gas byproduct to determineaspect ratio dependent selectivity.
 5. The method, as recited in claim1, further comprising changing a chamber setting based on the measuredconcentration of the at least one gas byproduct.
 6. The method, asrecited in claim 1, wherein the dry processing the substrate comprisesplasma etching the substrate or a stack over the substrate.
 7. Themethod, as recited in claim 1, wherein the dry processing the substratecomprises etching a silicon containing layer.
 8. The method, as recitedin claim 1, wherein the byproducts comprise at least one of SiF₄, SiCl₄,SiBr₄, COF₂, CO₂, CO and CF₄.
 9. The method, as recited in claim 1,wherein the using the concentration of the at least one gas byproduct todetermine etch selectivity.
 10. The method, as recited in claim 1,wherein the measuring a concentration of the at least one gas byproductcomprises using IR absorption with a multi-pass gas cell to measure theconcentration of at least one gas byproduct.
 11. The method, as recitedin claim 10, wherein the IR absorption measures the concentration of atleast one gas byproduct after the at least one gas byproduct is pumpedthrough an exhaust pump.
 12. The method, as recited in claim 1, whereinthe byproducts comprises SiF₄.
 13. A method for dry etching at leasteight alternating layers over a substrate in a processing chamber,comprising creating a plurality of concentration models related toprocessing rate and processing uniformity; placing the substrate in theprocessing chamber; dry etching the at least eight alternating layers,wherein the dry etching creates at least one gas byproduct; measuring aconcentration of the at least one gas byproduct; fitting the measuredconcentration of the at least one gas byproduct over time to at leastone of the plurality of concentration models; using the concentration ofthe at least one gas byproduct to determine etching rate of thesubstrate, etch selectivity, and etch uniformity; creating processparameters from the fitted at least one of the plurality ofconcentration models and the measured concentration of the at least onegas byproduct; using the created process parameters to determinerun-to-run and chamber-to-chamber performance; and changing a chamberparameter based on the measured concentration.